Cone beam CT (CBCT) technique provides true three-dimensional (3D) images of a breast; however, metal clips and
needles used for surgical planning can cause artifacts, which may extend to many adjacent slices, in the reconstructed
images obtained by the Feldkamp-Davis-Kress (FDK) filtered backprojection method,. In this paper, a sinogram
based method to remove the metal clips in the projection image data is described and discussed for improving the
quality of reconstructed breast images. First, the original projection data was reconstructed using the FDK algorithm
to obtain a volumetric image with metal clips and artifacts. Second, the volumetric image was segmented by using
the threshold method to obtain a 3D map of metal objects. Third, a forward projection algorithm is applied to the
metal object map to obtain projection map of metal objects. Finally, the original projection images and projection
map of metal objects are reorganized into sinograms for correction in the angular space on a pixel-by-pixel basis.
Cone beam CT images of a mastectomy breast specimen are used to demonstrate the feasibility of using this
technique for removal of metal object artifacts. Preliminary results have demonstrated that metal objects artifacts in
3D images were reduced and the image quality were improved.

In this study, we demonstrated the contrast-to-noise ratio (CNR) improvement in breast cone beam CT (CBCT) using the
volume-of-interest (VOI) scanning technique. In VOI breast CBCT, the breast is first scanned at a low exposure level. A
pre-selected VOI is then scanned at a higher exposure level with collimated x-rays. The two image sets are combined
together to reconstruct high quality 3-D images of the VOI. A flat panel detector based system was built to demonstrate
and investigate the CNR improvement in VOI breast CBCT. The CNRs of the 8 plastic cones (Teflon, Delrin,
polycarbonate, Lucite, solid water, high density polystyrene, nylon and polystyrene) in a breast phantom were measured
in images obtained with the VOI CBCT technique and compared to those measured in standard full field CBCT images.
CNRs in VOI CBCT images were found to be higher than those in regular CBCT images in all plastic cones. The mean
glandular doses (MGDs) from the combination of a high exposure VOI scan and a low exposure full-field scan was
estimated to be similar to that from regular full-field scan at standard exposure level. The VOI CBCT technique allows a
VOI to be imaged with enhanced image quality with an MGD similar to that from regular CBCT technique.

To study the effects of overlapping anatomy on microcalcification detection at various incident exposure levels. Images
of an anthropomorphic breast phantom (RMI 169) overlapping with simulated microcalcifications ranging from 150 to
212 &mu;m in size placed in two breast density regions, fatty and heterogeneously dense, were acquired with an a-Si/a-Se
flat panel based digital mammography system (Selenia) operated with Mo-Mo target/filter combination at 28 kVp. The
mammograms were exposed with 20, 30, 40, 60, 80, 120, 160, 240 and 325 mAs for varying the exposure level. A 4-AFC study was performed for evaluation of the detection performance. Four 400&times;400-pixel images were displayed as 2&times;2 array on a LCD flat panel based review workstation. One of the four images contained a cluster of five microcalcifications and was randomly placed in one of the four quadrants. A physicist was asked to select the image
containing the microcalcifications and to report the number of visible microcalcifications. The fraction of correct
responses was computed with two different criteria: (1) the selected images contained one or more microcalcifications,
and (2) the selected images contained 4 or 5 visible microcalcifications. The statistical significance of the differences in fractions for different exposure levels and regions was evaluated. The results showed that, if visibility of one or more
microcalcifications is required, the fractions of correct responses were 1 for all size groups and most exposure levels in
both fatty and heterogeneously dense regions. If a visibility of 80% or more of the microcalcifications was required, the
fractions of correct responses significantly decreased in both regions. The results indicated that microcalcification
detection in the fatty region appeared to be mainly limited by the quantum noise, and that in the heterogeneously dense region may be limited by both the anatomic noise and the quantum noise.

Registration and superimposition of images acquired from two different detectors is essential to dual-resolution cone
beam CT. In this study we implemented and tested a method of integration, which is to register and superimpose the high
resolution volume of interest (VOI) only images to the low resolution full field images. First, we acquired two images
sets: One is low exposure low resolution full field images acquired with a low resolution detector; the other is high
exposure high resolution volume of interest (VOI) images acquired with a high resolution detector and VOI mask. To
locate the VOI positions in full field images, the third images set with VOI mask but without phantom was acquired with the low resolution detector. In the third images set, high contrast VOI boundaries were located and used to determine positions of the VOI in full field images. Then high resolution VOI images were superimposed with the full field images to generate integrated images set. Integrated images set was tested by subtraction from full field images set and then used to reconstruct images using regular FDK algorithm. In the reconstructed images, five Al wires (as small as 152 &mu;m) can be clearly seen in the VOI.

In this study, we demonstrated volume of interest (VOI) scanning technique in dual resolution cone beam CT (CBCT)
breast imaging. A paraffin cylinder with a diameter of 130 mm was used to simulate breast. A wire phantom with a
diameter of 15 mm was constructed as VOI. The phantom contains 8 vertically aluminum wires of various diameters
surrounded by paraffin. The wire phantom was inserted into the breast phantom 45 mm away from the center. The
phantoms were first scanned with a bench top experimental CBCT system at a low exposure level with the detector
operated in a binning mode. Then a VOI mask was placed between the x-ray source and the phantoms. The phantoms
were scanned again with high exposure level and the detector operated in the non-binning mode. The VOI mask was
moved to follow the wire phantom during the whole CT scan to limit the exposures to cover the VOI only. The low
resolution and high resolution images were then combined together for reconstruction with FDK algorithm. Visual
review of the regular and dual resolution CBCT images shows that thinnest resolvable wire in the dual resolution CBCT
images has a diameter of 152 &mu;m. The thinnest resolvable wire in regular CBCT images has a diameter of 254 &mu;m. The
estimated dose to the phantom for dual resolution CBCT is 123% of that with regular CBCT at low exposure level. The dual resolution CBCT technique greatly enhances the CT image quality while still remains a low exposure level to the phantom.

Cone beam breast CT technique provides true three dimensional (3D) images of breast anatomy; however the
detectability of calcification is limited due to low exposure levels on each projection. In this study, we investigated the
possibility of using anisotropic exposure distributions to improve the visibility of calcifications in the breast CT images.
Our approach was to measure the CBCT projections with isotropic high and low exposures separately. Reconstruction
was performed upon different combinations of these two sets of projection sequences to investigate the visibility change
due to the limited-angle high exposure projections. Our preliminary results show that the visibility is improved with the
number of high exposure projections in the combinations. In the future we will measure the CBCT projections with
anisotropic exposures while keeping the total exposure constant.

Images of mastectomy breast specimens have been acquired with a bench top experimental Cone beam CT
(CBCT) system. The resulting images have been segmented to model an uncompressed breast for
simulation of various CBCT techniques. To further simulate conventional or tomosynthesis mammographic
imaging for comparison with the CBCT technique, a deformation technique was developed to convert the
CT data for an uncompressed breast to a compressed breast without altering the breast volume or regional
breast density. With this technique, 3D breast deformation is separated into two 2D deformations in coronal
and axial views. To preserve the total breast volume and regional tissue composition, each 2D deformation
step was achieved by altering the square pixels into rectangular ones with the pixel areas unchanged and resampling
with the original square pixels using bilinear interpolation. The compression was modeled by first
stretching the breast in the superior-inferior direction in the coronal view. The image data were first
deformed by distorting the voxels with a uniform distortion ratio. These deformed data were then deformed
again using distortion ratios varying with the breast thickness and re-sampled. The deformation procedures
were applied in the axial view to stretch the breast in the chest wall to nipple direction while shrinking it in
the mediolateral to lateral direction re-sampled and converted into data for uniform cubic voxels. Threshold
segmentation was applied to the final deformed image data to obtain the 3D compressed breast model. Our
results show that the original segmented CBCT image data were successfully converted into those for a
compressed breast with the same volume and regional density preserved. Using this compressed breast
model, conventional and tomosynthesis mammograms were simulated for comparison with CBCT.

In this work, we investigated the visibility of microcalcifications in CCD-based cone beam CT (CBCT) breast imaging.
A paraffin cylinder with a diameter of 135 mm and a thickness of 40 mm was used to simulate a 100% adipose breast.
Calcium carbonate grains, ranging from 140-150 to 200-212 &mu;m in size, were used to simulate the microcalcifications.
Groups of 25 same size microcalcifications were arranged into 5 &times; 5 clusters. Each cluster was embedded at the center of
a smaller (15 mm diameter) cylindrical paraffin phantom, which were inserted into a hole at the center of the breast
phantom. The breast phantom with the simulated microcalcifications was scanned on a bench top experimental CCDbased
cone beam CT system at various exposure levels with two CCD cameras: Hamamatsu's C4742-56-12ER and
Dalsa 99-66-0000-00. 300 projection images were acquired over 360&deg; and reconstructed with Feldkamp's backprojection
algorithm using a ramp filter. The images were reviewed by 6 readers independently. The ratios of visible
microcalcifications were recorded and averaged over all readers. These ratios were plotted as the function of measured
image signal-to-noise ratio (SNR) for various scans. It was found that 94% visibility was achieved for 200-212 &mu;m
calcifications at an SNR of 48.2 while 50% visibility was achieved for 200-212, 180-200, 160-180, 150-160 and 140-150
&mu;m calcifications at an SNR of 25.0, 35.3, 38.2, 42.2 and 64.4, respectively.

Breast density has been recognized as one of the major risk factors for breast cancer. However, breast
density is currently estimated using mammograms which are intrinsically 2D in nature and cannot
accurately represent the real breast anatomy. In this study, a novel technique for measuring breast density
based on the segmentation of 3D cone beam CT (CBCT) images was developed and the results were
compared to those obtained from 2D digital mammograms. 16 mastectomy breast specimens were imaged
with a bench top flat-panel based CBCT system. The reconstructed 3D CT images were corrected for the
cupping artifacts and then filtered to reduce the noise level, followed by using threshold-based
segmentation to separate the dense tissue from the adipose tissue. For each breast specimen, volumes of the
dense tissue structures and the entire breast were computed and used to calculate the volumetric breast
density. BI-RADS categories were derived from the measured breast densities and compared with those
estimated from conventional digital mammograms. The results show that in 10 of 16 cases the BI-RADS
categories derived from the CBCT images were lower than those derived from the mammograms by one
category. Thus, breasts considered as dense in mammographic examinations may not be considered as
dense with the CBCT images. This result indicates that the relation between breast cancer risk and true
(volumetric) breast density needs to be further investigated.

My Library

You currently do not have any folders to save your paper to! Create a new folder below.

Keywords/Phrases

Keywords

in

Remove

in

Remove

in

Remove

+ Add another field

Search In:

Proceedings

Volume

Journals +

Volume

Issue

Page

Journal of Applied Remote SensingJournal of Astronomical Telescopes Instruments and SystemsJournal of Biomedical OpticsJournal of Electronic ImagingJournal of Medical ImagingJournal of Micro/Nanolithography, MEMS, and MOEMSJournal of NanophotonicsJournal of Photonics for EnergyNeurophotonicsOptical EngineeringSPIE Reviews